Like everyone, I watched the destruction from Hurricane Ida unfold. It was a catastrophic storm that did exactly what we expect a strong Category 4 storm to do. Before the storm, New Orleans Mayor Latoya Cantrell and other officials indicated, based on National Weather Service consultation, that there was not enough time for mandatory evacuations. While Cantrell issued a mandatory evacuation for residents without levee protection, the forecast of a major hurricane came too late for a broader, mandatory evacuation of New Orleans. Hurricane Ida, like many recent storms, rapidly intensified. Do officials need a new evacuation playbook for an era of rapidly-intensifying hurricanes?
I was motivated to write this piece because my initial instincts were to defend the efficacy of the weather forecasts. By Thursday, the National Hurricane Center was forecasting a Category 2 storm at landfall, which is a pretty significant threat in itself. The National Hurricane Center public advisory on Thursday August 26th even said, “Additional strengthening is likely over the Gulf of Mexico and the system could be near major hurricane strength when it approaches the northern Gulf coast.” By Friday August 27th, forecasts were locked in on a major storm to make landfall on the southeastern Louisiana coast.
From that perspective, the meteorological forecast (track and intensity) was quite good. Forecasters mentioned the possibility of a major hurricane three days in advance of landfall, and more definitively, two days prior to the storm reaching the U.S. coastline. However, other colleagues raised counterpoints by noting that the time window of the upgraded forecast did not lend itself to a large-scale, mandatory evacuation. Jeff Adelson, a staff writer at The Times-Picayune and The Advocate, tweeted on August 28th, “Just for some context, this storm was too quick for mandatory evacuations in NOLA…. – city-assisted evacuation for 40k residents without vehicles takes 72hr minimum – Contraflow takes 12-24hr, minimum.”
Here’s the reality of the situation. Hurricane Ida did something extraordinary. It deepened 50 mb+ in 24 hours or less. That rate exceeds the threshold for “rapid deepening.” Rapid intensification is defined as a storm that has an increase in maximum sustained wind speeds of at least 35 mph in 24 hours or less. According to CNN meteorologist Brandon Miller and the National Hurricane Center, Ida strengthened by that amount in about 6 hours. Yikes!
In recent years, it seems that rapid intensification (RI) has become more frequent. Ten storms underwent RI during the 2020 season, but we also have to be careful not to be recency biased. However, a 2019 paper published in Nature suggested that rapid intensification events were trending upward and that natural variability alone was unable to explain the trend. However, the authors stopped short of attributing anthropogenic effects either. Another 2019 paper published in Environmental Research Letters examined connections between global warming and rapid intensification of typhoons in the Pacific Ocean. The jury is still somewhat out, but it certainly is plausible that warming oceans will support more RI events.
If this is the case, will officials need to adjust their playbook beyond this 48 to 72 hour threshold? As we have seen with several storms in recent years like Ida (2021) or Michael (2018), storms can gain intensity rapidly. We have known, within the meteorology community for some time now, that the skill of intensity forecasts lags behind the skill of track forecasts. Let’s review – RI events may be increasing and intensity forecasts lag track forecasts. Some questions that come to mind for me include:
- Do officials need to lower the threshold (perhaps Category 2 storms) to trigger action?
- Are there quick-turnaround options when large-scale, mandatory evacuations are off the table (Superdome option, for example)?
- What is the public tolerance for mandatory evacuations earlier in the event with the prospect that the worst-cast never happens (The “better safe than sorry” policy)?
- Do we need federal/state assistance or stipends for disaster evacuations to offset the disparities in who can afford to evacuate voluntarily?
At the end of the day, my meteorology community and public officials want the same thing. Hurricane Ida represents a clear example of good forecasting and bad timing. Remember, nature does not behave on our timelines (especially when we are also tinkering with the natural system too).